This invention relates generally to passivation of integrated circuits. More particularly, the present invention relates to passivation of integrated circuits containing ferroelectric devices with an extremely hard passivation layer, which can be ceramic as well as ferroelectric.
Typically, silicon dioxide and silicon nitride are used to passivate integrated circuits. These materials are the industry standards for passivating integrated circuits and are used effectively on many types of integrated circuits. A thick layer of chemical vapor deposited ("CVD") silicon nitride, while a preferred passivation material for most integrated circuits, cannot be used on integrated circuits that contain ferroelectric materials. The reason for this is that the conventional technique for CVD depositing silicon nitride includes the presence of hydrogen gas. Ferroelectric materials tend to degrade by losing their ferroelectric properties in the presence of hydrogen. For example, the performance of capacitors fabricated with a common ferroelectric material, lead zirconate titanate ("PZT"), is degraded in the presence of hydrogen. The integrated circuit package itself can also be a source of the undesirable hydrogen gas. It is possible to sputter silicon nitride as a passivation layer, but with the present state of the art, the quality of the resulting passivation layer in not equal to that of the CVD silicon nitride passivation layer. Thus, silicon dioxide is used as an alternative passivation material for ferroelectric integrated circuits. While silicon dioxide passivation can be used in many applications, it is not an ideal passivation material. Silicon dioxide does not provide a good barrier to hydrogen, or a barrier to mobile ion contamination from potassium, sodium, and other mobile ions. In addition, silicon dioxide does not substantially reduce mechanical stress applied to an integrated circuit during packaging, which can also degrade performance.
What is desired is an ideal passivating material for a ferroelectric integrated circuit that prevents hydrogen gas and mobile ion contamination and also has the structural integrity to substantially reduce stress during packaging.